Mercurial > hg
comparison rust/rhg/README.md @ 47779:6df528ed47a9 stable
rhg: Add build and config instructions to the README file
This adds documentation explaining how to compile, configure, and use rhg
as well as how the fallback mechanism works.
Differential Revision: https://phab.mercurial-scm.org/D11229
author | Simon Sapin <simon.sapin@octobus.net> |
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date | Thu, 29 Jul 2021 11:53:03 +0200 |
parents | cf04f62d1579 |
children | b1c20e41098f |
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47778:97acbced3a99 | 47779:6df528ed47a9 |
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1 # rhg | 1 # `rhg` |
2 | 2 |
3 This project provides a fastpath Rust implementation of the Mercurial (`hg`) | 3 The `rhg` executable implements a subset of the functionnality of `hg` |
4 version control tool. | 4 using only Rust, to avoid the startup cost of a Python interpreter. |
5 This subset is initially small but grows over time as `rhg` is improved. | |
6 When fallback to the Python implementation is configured (see below), | |
7 `rhg` aims to be a drop-in replacement for `hg` that should behave the same, | |
8 except that some commands run faster. | |
9 | |
10 | |
11 ## Building | |
12 | |
13 To compile `rhg`, either run `cargo build --release` from this `rust/rhg/` | |
14 directory, or run `make build-rhg` from the repository root. | |
15 The executable can then be found at `rust/target/release/rhg`. | |
16 | |
17 | |
18 ## Mercurial configuration | |
19 | |
20 `rhg` reads Mercurial configuration from the usual sources: | |
21 the user’s `~/.hgrc`, a repository’s `.hg/hgrc`, command line `--config`, etc. | |
22 It has some specific configuration in the `[rhg]` section: | |
23 | |
24 * `on-unsupported` governs the behavior of `rhg` when it encounters something | |
25 that it does not support but “full” `hg` possibly does. | |
26 This can be in configuration, on the command line, or in a repository. | |
27 | |
28 - `abort`, the default value, makes `rhg` print a message to stderr | |
29 to explain what is not supported, then terminate with a 252 exit code. | |
30 - `abort-silent` makes it terminate with the same exit code, | |
31 but without printing anything. | |
32 - `fallback` makes it silently call a (presumably Python-based) `hg` | |
33 subprocess with the same command-line parameters. | |
34 The `rhg.fallback-executable` configuration must be set. | |
35 | |
36 * `fallback-executable`: path to the executable to run in a sub-process | |
37 when falling back to a Python implementation of Mercurial. | |
38 | |
39 * `allowed-extensions`: a list of extension names that `rhg` can ignore. | |
40 | |
41 Mercurial extensions can modify the behavior of existing `hg` sub-commands, | |
42 including those that `rhg` otherwise supports. | |
43 Because it cannot load Python extensions, finding them | |
44 enabled in configuration is considered “unsupported” (see above). | |
45 A few exceptions are made for extensions that `rhg` does know about, | |
46 with the Rust implementation duplicating their behavior. | |
47 | |
48 This configuration makes additional exceptions: `rhg` will proceed even if | |
49 those extensions are enabled. | |
50 | |
51 | |
52 ## Installation and configuration example | |
53 | |
54 For example, to install `rhg` as `hg` for the current user with fallback to | |
55 the system-wide install of Mercurial, and allow it to run even though the | |
56 `rebase` and `absorb` extensions are enabled, on a Unix-like platform: | |
57 | |
58 * Build `rhg` (see above) | |
59 * Make sure the `~/.local/bin` exists and is in `$PATH` | |
60 * From the repository root, make a symbolic link with | |
61 `ln -s rust/target/release/rhg ~/.local/bin/hg` | |
62 * Configure `~/.hgrc` with: | |
63 | |
64 ``` | |
65 [rhg] | |
66 on-unsupported = fallback | |
67 fallback-executable = /usr/bin/hg | |
68 allowed-extensions = rebase, absorb | |
69 ``` | |
70 | |
71 * Check that the output of running | |
72 `hg notarealsubcommand` | |
73 starts with `hg: unknown command`, which indicates fallback. | |
74 | |
75 * Check that the output of running | |
76 `hg notarealsubcommand --config rhg.on-unsupported=abort` | |
77 starts with `unsupported feature:`. |